man/sd_notify.xml

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  23
  24 <refentry id="sd_notify">
  25
  26         <refentryinfo>
  27                 <title>sd_notify</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>sd_notify</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd_notify</refname>
  47                 <refname>sd_notifyf</refname>
  48                 <refpurpose>Notify service manager about start-up completion and other daemon status changes</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <funcsynopsis>
  53                         <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  54
  55                         <funcprototype>
  56                                 <funcdef>int <function>sd_notify</function></funcdef>
  57                                 <paramdef>int <parameter>unset_environment</parameter></paramdef>
  58                                 <paramdef>const char *<parameter>state</parameter></paramdef>
  59                         </funcprototype>
  60
  61                         <funcprototype>
  62                                 <funcdef>int <function>sd_notifyf</function></funcdef>
  63                                 <paramdef>int <parameter>unset_environment</parameter></paramdef>
  64                                 <paramdef>const char *<parameter>format</parameter></paramdef>
  65                                 <paramdef>...</paramdef>
  66                         </funcprototype>
  67                 </funcsynopsis>
  68         </refsynopsisdiv>
  69
  70         <refsect1>
  71                 <title>Description</title>
  72                 <para><function>sd_notify()</function> shall be called
  73                 by a daemon to notify the init system about status
  74                 changes. It can be used to send arbitrary information,
  75                 encoded in an environment-block-like string. Most
  76                 importantly it can be used for start-up completion
  77                 notification.</para>
  78
  79                 <para>If the <parameter>unset_environment</parameter>
  80                 parameter is non-zero <function>sd_notify()</function>
  81                 will unset the <varname>$NOTIFY_SOCKET</varname>
  82                 environment variable before returning (regardless
  83                 whether the function call itself succeeded or
  84                 not). Further calls to
  85                 <function>sd_notify()</function> will then fail, but
  86                 the variable is no longer inherited by child
  87                 processes.</para>
  88
  89                 <para>The <parameter>state</parameter> parameter
  90                 should contain an newline-separated list of variable
  91                 assignments, similar in style to an environment
  92                 block. A trailing newline is implied if none is
  93                 specified. The string may contain any kind of variable
  94                 assignments, but the following shall be considered
  95                 well-known:</para>
  96
  97                 <variablelist>
  98                         <varlistentry>
  99                                 <term>READY=1</term>
 100
 101                                 <listitem><para>Tells the init system
 102                                 that daemon startup is finished. This
 103                                 is only used by systemd if the service
 104                                 definition file has Type=notify
 105                                 set. The passed argument is a boolean
 106                                 "1" or "0". Since there is little
 107                                 value in signalling non-readiness, the
 108                                 only value daemons should send is
 109                                 "READY=1".</para></listitem>
 110                         </varlistentry>
 111
 112                         <varlistentry>
 113                                 <term>STATUS=...</term>
 114
 115                                 <listitem><para>Passes a single-line
 116                                 status string back to the init system
 117                                 that describes the daemon state. This
 118                                 is free-form and can be used for
 119                                 various purposes: general state
 120                                 feedback, fsck-like programs could
 121                                 pass completion percentages and
 122                                 failing programs could pass a human
 123                                 readable error message. Example:
 124                                 "STATUS=Completed 66% of file system
 125                                 check..."</para></listitem>
 126                         </varlistentry>
 127
 128                         <varlistentry>
 129                                 <term>ERRNO=...</term>
 130
 131                                 <listitem><para>If a daemon fails, the
 132                                 errno-style error code, formatted as
 133                                 string. Example: "ERRNO=2" for
 134                                 ENOENT.</para></listitem>
 135                         </varlistentry>
 136
 137                         <varlistentry>
 138                                 <term>BUSERROR=...</term>
 139
 140                                 <listitem><para>If a daemon fails, the
 141                                 D-Bus error-style error code. Example:
 142                                 "BUSERROR=org.freedesktop.DBus.Error.TimedOut"</para></listitem>
 143                         </varlistentry>
 144
 145                         <varlistentry>
 146                                 <term>MAINPID=...</term>
 147
 148                                 <listitem><para>The main pid of the
 149                                 daemon, in case the init system did
 150                                 not fork off the process
 151                                 itself. Example:
 152                                 "MAINPID=4711"</para></listitem>
 153                         </varlistentry>
 154
 155                         <varlistentry>
 156                                 <term>WATCHDOG=1</term>
 157
 158                                 <listitem><para>Tells systemd to
 159                                 update the watchdog timestamp. This is
 160                                 the keep-alive ping that services need
 161                                 to issue in regular intervals if
 162                                 <varname>WatchdogSec=</varname> is
 163                                 enabled for it. See
 164                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 165                                 for details. It is recommended to send
 166                                 this message if the
 167                                 <varname>WATCHDOG_USEC=</varname>
 168                                 environment variable has been set for
 169                                 the service process, in every half the
 170                                 time interval that is specified in the
 171                                 variable.</para></listitem>
 172                         </varlistentry>
 173                 </variablelist>
 174
 175                 <para>It is recommended to prefix variable names that
 176                 are not shown in the list above with
 177                 <varname>X_</varname> to avoid namespace
 178                 clashes.</para>
 179
 180                 <para>Note that systemd will accept status data sent
 181                 from a daemon only if the
 182                 <varname>NotifyAccess=</varname> option is correctly
 183                 set in the service definition file. See
 184                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 185                 for details.</para>
 186
 187                 <para><function>sd_notifyf()</function> is similar to
 188                 <function>sd_notify()</function> but takes a
 189                 <function>printf()</function>-like format string plus
 190                 arguments.</para>
 191         </refsect1>
 192
 193         <refsect1>
 194                 <title>Return Value</title>
 195
 196                 <para>On failure, these calls return a negative
 197                 errno-style error code. If
 198                 <varname>$NOTIFY_SOCKET</varname> was not set and
 199                 hence no status data could be sent, 0 is returned. If
 200                 the status was sent these functions return with a
 201                 positive return value. In order to support both, init
 202                 systems that implement this scheme and those which
 203                 don't, it is generally recommended to ignore the return
 204                 value of this call.</para>
 205         </refsect1>
 206
 207         <refsect1>
 208                 <title>Notes</title>
 209
 210                 <para>These functions are provided by the reference
 211                 implementation of APIs for new-style daemons and
 212                 distributed with the systemd package. The algorithms
 213                 they implement are simple, and can easily be
 214                 reimplemented in daemons if it is important to support
 215                 this interface without using the reference
 216                 implementation.</para>
 217
 218                 <para>Internally, these functions send a single
 219                 datagram with the state string as payload to the
 220                 AF_UNIX socket referenced in the
 221                 <varname>$NOTIFY_SOCKET</varname> environment
 222                 variable. If the first character of
 223                 <varname>$NOTIFY_SOCKET</varname> is @ the string is
 224                 understood as Linux abstract namespace socket. The
 225                 datagram is accompanied by the process credentials of
 226                 the sending daemon, using SCM_CREDENTIALS.</para>
 227
 228                 <para>For details about the algorithms check the
 229                 liberally licensed reference implementation sources:
 230                 <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
 231                 resp. <ulink
 232                 url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
 233
 234                 <para><function>sd_notify()</function> and
 235                 <function>sd_notifyf()</function> are implemented in
 236                 the reference implementation's
 237                 <filename>sd-daemon.c</filename> and
 238                 <filename>sd-daemon.h</filename> files. These
 239                 interfaces are available as shared library, which can
 240                 be compiled and linked to with the
 241                 <literal>libsystemd-daemon</literal>
 242                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 243                 file. Alternatively, applications consuming these APIs
 244                 may copy the implementation into their source tree. For
 245                 more details about the reference implementation see
 246                 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 247
 248                 <para>If the reference implementation is used as
 249                 drop-in files and -DDISABLE_SYSTEMD is set during
 250                 compilation these functions will always return 0 and
 251                 otherwise become a NOP.</para>
 252         </refsect1>
 253
 254         <refsect1>
 255                 <title>Environment</title>
 256
 257                 <variablelist>
 258                         <varlistentry>
 259                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 260
 261                                 <listitem><para>Set by the init system
 262                                 for supervised processes for status
 263                                 and start-up completion
 264                                 notification. This environment variable
 265                                 specifies the socket
 266                                 <function>sd_notify()</function> talks
 267                                 to. See above for details.</para></listitem>
 268                         </varlistentry>
 269                 </variablelist>
 270         </refsect1>
 271
 272         <refsect1>
 273                 <title>Examples</title>
 274
 275                 <example>
 276                         <title>Start-up Notification</title>
 277
 278                         <para>When a daemon finished starting up, it
 279                         might issue the following call to notify
 280                         the init system:</para>
 281
 282                         <programlisting>sd_notify(0, "READY=1");</programlisting>
 283                 </example>
 284
 285                 <example>
 286                         <title>Extended Start-up Notification</title>
 287
 288                         <para>A daemon could send the following after
 289                         completing initialization:</para>
 290
 291                         <programlisting>sd_notifyf(0, "READY=1\n"
 292               "STATUS=Processing requests...\n"
 293               "MAINPID=%lu",
 294               (unsigned long) getpid());</programlisting>
 295                 </example>
 296
 297                 <example>
 298                         <title>Error Cause Notification</title>
 299
 300                         <para>A daemon could send the following shortly before exiting, on failure</para>
 301
 302                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 303               "ERRNO=%i",
 304               strerror(errno),
 305               errno);</programlisting>
 306                 </example>
 307         </refsect1>
 308
 309         <refsect1>
 310                 <title>See Also</title>
 311                 <para>
 312                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 313                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 314                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 315                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 316                 </para>
 317         </refsect1>
 318
 319 </refentry>